#include<stdio.h>
int main(){
	int n=1;
	double x,y,sum = 1;
	scanf("%lf",&x);
	y = x;
	do{
		sum += y;
		n++;
		y = y*x / n;
	}while(y > 0.00001);
	sum += y;
	printf("%.4lf",sum);
	
	return 0;
}
